Re: [PATCH] pci: assert configuration access is within bounds

[Michael S. Tsirkin]

On Thu, Jun 04, 2020 at 05:36:31PM +0100, Dr. David Alan Gilbert wrote:
> * P J P (ppandit@redhat.com) wrote:
> > From: Prasad J Pandit <pjp@fedoraproject.org>
> > 
> > While accessing PCI configuration bytes, assert that
> > 'address + len' is within PCI configuration space.
> > 
> > Generally it is within bounds. This is more of a defensive
> > assert, in case a buggy device was to send 'address' which
> > may go out of bounds.
> 
> Can a guest trigger this assert?
> 
> Dave

Shouldn't be able to, no.

> > Suggested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> > Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> > ---
> >  hw/pci/pci.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > Update v1: defensive assert as separate patch
> >   -> https://lists.gnu.org/archive/html/qemu-devel/2020-06/msg00957.html
> >   -> https://lists.gnu.org/archive/html/qemu-devel/2020-06/msg00960.html
> > 
> > diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> > index 70c66965f5..7bf2ae6d92 100644
> > --- a/hw/pci/pci.c
> > +++ b/hw/pci/pci.c
> > @@ -1381,6 +1381,8 @@ uint32_t pci_default_read_config(PCIDevice *d,
> >  {
> >      uint32_t val = 0;
> >  
> > +    assert(address + len <= pci_config_size(d));
> > +
> >      if (pci_is_express_downstream_port(d) &&
> >          ranges_overlap(address, len, d->exp.exp_cap + PCI_EXP_LNKSTA, 2)) {
> >          pcie_sync_bridge_lnk(d);
> > @@ -1394,6 +1396,8 @@ void pci_default_write_config(PCIDevice *d, uint32_t 
> > addr, uint32_t val_in, int
> >      int i, was_irq_disabled = pci_irq_disabled(d);
> >      uint32_t val = val_in;
> >  
> > +    assert(addr + l <= pci_config_size(d));
> > +
> >      for (i = 0; i < l; val >>= 8, ++i) {
> >          uint8_t wmask = d->wmask[addr + i];
> >          uint8_t w1cmask = d->w1cmask[addr + i];
> > -- 
> > 2.26.2
> > 
> > 
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK